This invention relates to the recovery of non-ferrous metals from sulfide ores containing nickel, cobalt, copper and other nonferrous metals, and more particularly, it relates to the recovery of these metals from sulfide ore concentrates by the acidic leaching of these concentrates in the presence of oxygen at high temperatures and pressures. Specifically, this invention relates to the oxidative leaching of iron-containing sulfide ores, such as chalcopyrites, at high temperatures and pressures wherein neutralizing agents are employed to neutralize at least a portion of the free acid present in the concentrate slurry being processed.
In existing autoclave processes for the high temperature-high pressure treatment of sulfide ore concentrates for the recovery of metal values by oxidative leaching it is often desirable to neutralize a portion of the acidity produced as a result of the reactions that take place in the process. Normally, alkaline-earth metal neutralizing agents, such as lime or limestone, are used for this purpose. In some instances this neutralization is carried out after the oxidation-leaching step in a vessel separate from that of the main oxidation-leaching reaction. In other instances the slurry is removed from the autoclave, neutralized with the lime or limestone, and then returned to the autoclave for further processing. Alternatively, the neutralizing agent may be added directly to the leaching vessel. The neutralization of oxidized sulfide slurries with lime or limestone is described in U.S. Pat. Nos. 2,686,114 and 2,718,455.
Because of cost considerations, limestone is usually the preferred neutralizing agent. When limestone is used, however, carbon dioxide is produced which tends to dilute the gases that are used for oxidation. In order to prevent a buildup of CO.sub.2 in the system the CO.sub.2 must be bled off. Since the CO.sub.2 is distributed throughout the vapor space of the autoclave system, this bleeding is accompanied by losses of valuable oxygen. Likewise, it is usually necessary in these processes to control the prescribed operating temperatures, which, as a result of the exothermic nature of the oxidation reactions, tend to rise quite rapidly. In order to do this it then becomes necessary to remove heat from the system. This is commonly done by venting the vapors to the atmosphere with the consequent loss of the oxygen present in the vapors. Still in other instances the slurry is removed from the autoclave, cooled in a separate operation, and then returned to the autoclave system. Such methods are for the most part inefficient and wasteful and are not without a number of disadvantages.
It is the object of this invention to provide an autoclave system for the effective oxidation-leaching of sulfide ore concentrates without the disadvantages associated with conventional autoclave systems which have been used heretofore for the treatment of these concentrates.